Vehicle tires, particularly pneumatic or semi-pneumatic tires, are often reinforced by means of cords consisting of twisted or cabled brass-coated steel filaments. The twisted or cabled filaments consist of a series of individual wires. The wires are frequently high-carbon steel coated with a thin layer of alpha brass. After the steel wire has been electroplated with the brass coating, it is cold drawn to form a filament and subsequently stranded and/or cabled to form the cord.
Tire cord made from brass-plated steel wire requires special care during factory processing to minimize surface contamination. Plated steel wires are generally subject to corrosion of the steel substrate and oxidation of the brass coating, particularly if improperly handled or stored prior to incorporation into a rubber composite which is ultimately shaped to a molded article such as pneumatic tire. Corrosion and oxidation can also be caused from other external agents or elements in an environment where the cord is a reinforcement such as in a rubber composite. Such corrosion and oxidation can result in poor adhesion between the cords and rubber which, in turn, can result in a failure of the reinforcement in the rubber composite or can cause degradation of a good adhesive bond during service life of the composite. Clean, untreated brass-coated steel wire will normally have sufficient good initial adhesion to the adjacent rubber. However, the adhesion usually will drop with time, i.e., with aging due to heat, stress and/or chemical degradation or corrosion effects. Various additives described in the literature have in certain instances shown improved initial and aged adhesion. Unfortunately; such additives have often not proved entirely satisfactory either due to required complexities in their preparation or the mixed results realized from their use. Organic corrosion inhibitors are usually applied to the finished cabling by immersion into a water or other organic solvent containing the inhibitor or by vapor treatment. These procedures require additional equipment and processing time. Therefore, there exists a need for a method of treating brass-plated steel wire which protects the bare metallic surface from corrosion and concomitantly improves the initial and aged adhesion of the wire to the rubber environment within the vulcanized composite.